HSK 4
回信
huíxìn动名
to reply; to write back; letter written in reply
我把回信放进了书包里。
Wǒ bǎ huí xìn fàng jìn le shū bāo lǐ.
I put the reply in my schoolbag.
Say it
Hold the button, say it, then let go.
Other HSK words sharing a character
Also free:
New in the HSK 3.0 word list at level 4.